Hydraulic steering motor and shimmy dampener for airplane landing gear wheels



Apnl 3, 1945. H. CHISHOLM, JR Y 2,372,710

HYDRAULIC STEERING MOTOR AND SH'IMMY DAMPENER FOR AIRPLANE LANDING GEARWHEELS 5 Sheets-Sheet 1 Filed Dec. 11, 1941 TICKET-L flqeer A. C aw/o4,dew

Aprll 3, 1945. .H. CHISHOLM, JR z372,710

HYDRAULIC STEERING MOTOR AND SHIMMY DAMPENER I FOR AIRPLANE LANDING GEARWHEELS Filed Dec. 11, 1941 5 Sheets-Sheet 2 DAMPENER R AIRPL E LAND G RWHEELS April 3, 1945. H. L. HISHOLM, JR 2,372,710

HYDRAULIC STEERI MOTOR AND SHIMMY Fil D60. 1 5 Sheets-Sheet 3 mA/W ' p3} 1945- H. L. HISHOLM, JR 2,372,710

TOR AND SHIMMY DAMPENER HYDRAULIC ERI MO FOR PLANE LANDI GEAR WHEELSFiled Dec. 1941 5 Sheets-Sheet 4 ZITYEWZQP Apnl 3, 1945. H. CHISHOLM. JR2,372,710

HYDRAULIC STEERING MOTOR AND SHIMMY DAMPENER FOR AIRPLANE LANDING GEARWHEELS Filed Dec..1l, 1941 5 Sheets-Sheet s W3 8 w .2 IIYK 3 3 E. V1 7 rw mm f 1 WV//// 7/7/% m QIIIIIIIIIIIIIWIIIIIIW Patented Apr. 3, 1945HYDRAULIC STEERIN MY DAMPENER FOR GEAR WHEELS Harry L. Chisholm, Jr.,Buflalo, N.

by mesne assignments,

Corporation, Detroit,

Michigan G MOTOR AND SHEI- AIRPLANE LANDING Y., assignor, toHoudaille-Hershey Mich, a corporation of Application December 11, 1941,Serial No. 422,486

1 Claims. (01. 121-41) a hydraulic device for the purpose referredtowhich receives its hydraulic power from the hydraulic system nowgenerally used on airplanes for control of wing flaps, the retraction ofthe landing gear, and for other controls and adjust ments.

Another important object is to utilize a hydraulic device substantiallyin the form of a, ro-

element is connected with the steering wheel and subjected to hydraulicpressure for effecting steering movement of the wheel, with the valvemechanism of the device adjustable by the pilot for selective hydraulicmovement of the piston structure and steering movement of the wheels.

Still another object is to provide such arrangement and operation of thevalving structure that any attempted shimmying movement of the wheel andthe piston structure to which it is connected will result in hydraulicfluid control in the hytary hydraulic shock absorber in which thepiston.

draulic device for dampening and stopping the shimmying.

Further objects of the invention are to provide for control of thehydraulic fluid under varying conditions so as toprotect the structureagainst undue strain without interfering with its proper functioning tosteer and dampen out shimmying.

All the various features -of my invention are embodied in the structureshown on the drawings, in which drawings:

Figure 1 is a side elevation of a steering wheel supporting structureand its connection with an airplane and showing my improved hydraulicdevice applied thereto;

Figure 2 is an enlarged section on plane II-II of Figure 1;

Figure 3 is an enlarged section on plane III-J11 of Figure 1 and alsoplane III-III of Figure 4;

Figure 4 is a section on plane IV-IV of Figure 3, the valve being in oneof its steering setting positions Figure 5 is a section similar toFigure 4 showing the valve in position for shutting off steeringproducing flow;

Figure 6 is a transverse section of the hydraulic device showing theapplication of blow-off valves;

Figure 'l is a section on plane VII-VII of Figure 6;

Figure 8 is a section like Figure 3 butshowing a modified form of valveassembly;

Figure 9 is a section on plane.IX-1x 8; and

Figure 10 is a section on plane X-'-X of Figure 8. l

Referring to Figure 1, A indicates the body structure of an airplanefrom which extends an oleo strut 0 whose cylinder member 10 is hinged tothe airplane body as indicated at I l and whose plunger or pistonelement 12 terminates in a. fork I3 joumalling the wheel W to becontrolled. The oleo strut is well known in the art, the cylinder Illcontaining spring means or hydraulic fluid flow resistingmeans fordampening the movement of the piston or plunger element i2 for absorbingthe shock of vertical movement of the wheel W. Upper and lower links I4and I5 hinged together at their outer ends have their inner endsconnected respectively to the fork l3 and to the cylinder element l0,and where the fork supporting plunger element I2 is to be held againstrotary movement, the upper link ll will be secured to the cylinderelement against rotary movement relative thereto. However, where theplunger element is to be rotatable, as in connection with my invention,the upper link I4 is pivoted at its inner end to a ring l8 joumaledbetween collars l1 and I8 rigidly secured to the cylinder III. The strutor brace structure l9 extends between the airplane body and the cylinderl0.

of Figure The hydraulic controlling device H for the wheel comprises a,cylinder structure C, a piston structure P, and valve structure V. Thecylindrical wall IQ of the cylinder structure has at its lower endears'2l l extending therefrom, and the collar I'I secured to thecylinder J0 of the oleo strut has ears 2| to which the ears 20 aresecured as'by bolts 22 for support of the cylinder structure C of thehydraulic device.

The piston structure P has the shaft 23 extending downwardly out of thecylinder structure and an arm 24 secured to the outer end of the shafthas its outer end connected by a link 25 with the outer end of an arm 28extending from the ring l6 which is rotatable on the oleo strut cylinderill. The piston structure of the hydraulic device the Working chambersto the ing the bore 48 extending therethrough ture forldesired hydraulicand the piston or plunger structure l2 of the oleo strut are thusconnected to rotate together:-.

The wall l9 of the cylinder structure C has up- D r and lower internalshoulders 21 and 29 against whichabut the cylinder end or closin walls29 and 30 respectively. An upper clamping wall 3ihas threaded engagementwith the end of the cylinder wall for clamping the endwall 26 securelyagainst the shoulder 21.. A clamping wall 32 has threaded engagement inthe lower end of the cylinder wall l9 andthrough an intermediate wall 33exerts pressure against the end wall 39 for holding this end wallsecurely against the shoulder 26. The cylinder wall l9 and its end walls29 and 36 define a cylinder space in which the piston structure Poperates.

Extending radially from opposite sides of the cylinder wall i9 andbetween the end walls 29 -.ments 34 and 34', defining hydraulic workingchambers 36, 36'-and 39, 39'. The piston shaft 23 is journaled in theend wall 36 and the intermediate wall 32, and the lower clamping wall 32surrounds the shaft and has a recess for suitable packing 46 intimatelyheld to the shaft by a plate 4| under pressure of a spring 42. Packingmaterial 43 is interposed between the clamping wall 32 and theintermediate wall 33 at'theperipheries thereof, these packingspreventing leakage from draulic device.

away to leave annular channels 6! and 62 respectively. I

Referring .to' Figures 4 and 5, the valve body on opposite sides thereofisjslabbed of! to leave segmental spaces 63 and 64 which communicaterespectively with the annular channels Gland 62, the spaces 63 and 64functioning as valve ports. Extending diametrally through the valve bodyparallel with the slabbed sides thereof is the port 65 which intersectsand communicates with the valve structure bore 46. The hydraulic workingchambers 39 and 39' are connected with the valve chamber by passageways66 and 66' through the piston hub, while the working chamber's 39 and39' areconnected with the valvechamber by passageways 61 and 61'respectively as clearly shown on Figs. 4 and 5. These passageways are sospacedthat when the valve body is in its neutral or normal position asshown on Fig. 5, the passageways will be shut oil from the valve chamberand the valve port 66 will be closed by v the piston hub wall. -When thevalve structure exterior of the hy- The piston shaft 2: has the bore 44there- 7 through communicatingat its inner end with 'a,

larger bore inthe piston hub 36 to form a cylindrlcal valve chamber 45..Within this bore and valve chamber is the valve structure V whose valvehead: 46 is operable in' the valve chamber with the stem 41 extendingtherefrom through the bore 44 in the shaft, the valve structure havfromone end to thexother and communicating at its lower end with a conduitor pipe '49. held to the end-- of the valve stem by a suitable coupling66. The valve structure is rotatable relative to the piston structureand a suitable stufilng box 6| in the outer end of the shaftsurrounds-the valve stem. At its outer end the valve stem has an arm 62extending therefrom whic ures l and 2, has a flexible cable its end byasultable fitting 64, ing to the cockpit of the airplane formanipulation by suitable means to I control. A guide and protectingsheath 66 is" preferably provided for the cable and isseated in andsecured to asuitable fitting 66 on the supporting collar I! for thehydraulic device H. i

Extending through an axial openingintheend wall 29 is a plug whichprojects into the upper end of the valve chamber 49 to for the upper endof the piston hub. the plug as best shown on Fig- 63 connected to thecable extend-" is rotated to a working position, as shown on Fig.- 4,the passagewaysfor one set of working" chambers will be connected withthe valve chamber and the passageways for the other set of working 1chambers will be in communication with thevalve port 66.

' I The upper clamping, wall 3| isrecessed in its lower side to leavethe closed space 66 between the wall 3| and the end wall 2:. a hydraulicfluid fiow pipe communicating with this space, and passageways 10through theplugll connecting this space with the annular channel 6| andwith g the valve ports 63 and 64.

The lower end wall 36 is recessed on its outer sidet'o leave a space Hbetween the end wall and the intermediate wall 32, this spacecommunicatingiwith a passageway 12 through the piston shaft and hubwhich passageway at its upper end communicates with the annular channel62 and the valve ports 63 and 64. The pipe 69 connects with a source ofhydraulic fluid under pressure and during operation of the hydraulicdevice this hydraulic pressure will be equal in the spaces 98 I and Hagainst the cylinder endwalls 29 and 36 so that the pressure against theinner and outer sides of these-end walls is at all times balanced.Referring to Figure 1, the pipe 69 is connected to receive hydraulicfluid under pressure from a source such as a pump 8.; This may be aseparate pump or may be the pump which supplies hydraulic pressure foroperation of other controls on the airplane. The pump draws hydraulicfluid from a reservoir R to which the pipe 66 from the hydraulic device'H "extends.

IA. suitable control valve 13: is"preferably included in the pipe 69,and also a check valve I4 for shutting off flow from rotate the valvestrucprovide a bearing having the axial recess 66. receiving'the upperend of the valve stem to provide a bearing therefor.

The valve body 46 has upper and lower shoulwardly of these shoulders thevalve body is cut the hydraulic pump " The opposite valve ports 63 and64 are always lunder the same pressure of the fluid fiow.from

the pipe 69 so that the valve structure is balanced i y, and the valvestem at its ends is always.

subjected to atmospheric pressure of the hydrauforward travel of theplane on the ground. With this position of the wheel the valve will bein its neutral position asshown on Figure 5, the valve device throughthepipe as to the port "being closed and the passageways between thehydraulic working chambers and the valve chamber being shut oil by thevalve body, the passageway edges being slightly overlapped by the valvebody so as to afford a seal against leakage. The hydraulic fluid in theworking chambers will now be blocked against any escape and the wheelwill be held hydraulically in its neutral or straight forward position.Due to resilience in the piston shaft, the piston shaft lever, and theconnecting linkage, a resonant shimmy of the wheel may occur, and inorder to prevent straining of the parts, relief passageways may beprovided which, as shown on Figs. 4 and 5, may be in the form oforifices 15 in disks l6 interposed in passageways TI through the pistonvanes or, as shown, through the abutments 31 and 31'. This resonantshimmy of the wheel will cause correspondin rotation of the pistonstructure. but f this shimmy movement is of sufliclent magnitude formovement of the piston structure relative to the valve to open thehydraulic working chamber passageways controlled by the valve, thenhydraulic fluid under pressure will immediately flow to return thepiston structure back to passageway closing position. Referring to Fig.5, if a shimmy movement of the wheel and the piston structure connectedthe valve. The location of the stop pins II and I8 on the piston shaftlever must of course then be set so that they will be equi-distancesfrom the valve lever abutment I9 when the valve is in normal position.

Assume now that the pilot desires to steer the wheel towards the leftfrom its forward running position shown on Figure 1. He will then setthe valve in counter-clockwise direction as shown on Figure 4. Suchsetting may be quickly made to the full limit of movement of the valve,or may be more slowly accomplished. If the valve is suddenly set to theposition shown on Figure 4, the working chamber passageways with thevalve chamber will be quickly opened for fluid flow under pressure fromthe valve ports 63 and -64 through the passageways 61 and 61' into theworking chambers 39 and 39' so that the fluid pressure, acting againstthe piston vanes, will rotate the piston structurein counter-clockwisedirection, and through the-lever linkage connection between the pistonstructure and the wheel fork, the wheel will be turned the correspondingdistance toward the left. The quick setting movement of the valve 'willstop when the valve lever abutment engaged the stop pin 18, and theresulting follow up movement of the piston structure therewith is inclockwise direction a distance beyond the overlap of the passagewayedges by the valve body, then hydraulic fluid under pressure will flowfrom the valve ports 83 and 64 into the working chambers 39: and 39,respectively,

If it is desired to steer the wheel w, the operator manipulates thecable 53 for swing of the lever 52 for rotary setting of the valvestructure. Such settingv of the valve structure in either direction fromthe neutral position will connect the valve ports 63 and 64 for flow ofhydraulic fluid under pressure to the corresponding working returns theworkin chamber passageways to a position relative to the valve forclosure of the passageways and closure of the valve port 85.-

If no further setting is then made of the valve, the hydraulic fluidwill be locked in the working chambers andthe wheel will be held in itssteering set position. If further steering movement of the wheel isdesired toward the left, the valve is correspondingly set in thatdirection and the hydraulic fluid under pressure through the openpassageways will act against the piston for follow up thereof. Forsteering in the opposite direction, the valve is set in thecorresponding direction and the piston structure and the valve will becaused by hydraulic pressure to follow the valve setting movement.

If the steering is to be more gradual, the valve will be slow y setfor'more gradual openings'of l the various passageways and ports so thatthe chambers, and the valve port 65 will connect the 1 other workingchambers with the return circuit through the valve stem 48, the pressureagainst the piston vanes causing the piston structure and the wheel tofollow the movements of the valve.

The rotational setting of the valve relative to the piston structure islimited in either direct on from its neutral position shown onFigure 5to a distance which will bring the valve port 55 into full communicationwith either setof passageways to the working chambers. Such limitationmay be accomplished by means of stop pins ll and I8 extending downwardlyfrom the hub of the lever which is secured to the piston shaft. anabutment 19 on the lever 52 extending from the valve structure beingmidway between these pins when the valve is in its normal or closed'position so that when the valve lever is swung in either direction intoengagement 'with the corresponding stop pin, the valve will be fullyopen. The valve lever 52 may be adjustable so that it may be 'set on thevalve stem to extend at any angle therefrom when the valve is in itsnormal position, so that the cable connection to the valve lever mayeiliciently swing the lever for setting of chambers.

wheel will correspondingly follow the valve .setting movements forgradual steering movements thereof. Thus, so long as the settingmovement of the valve continues, the piston structure and movement ofthe valve, the follow up movement of t e piston structure and wheel willeffect closure of the various passageways to the working chambers, andclosure of the valve port 65, so that t e hydraulic device will thenfunction to hold the wheel in .its set steering position, and to dampenany shimmy movement thereof in a manner which has already beenexplained. The restricted orifices for dampening resonant shimmy ofsmall magnitude when the valve is closed. will not require usage ofhydraulic fluid from the control system because the fluid in thehydraulic working chambers is entirely enclosed against flow exceptbetween adjacent working A slightloss through these orifices may occurduring short periods while the. direction of the Wheel is being changedin steering. but such slight loss will not materially effect the properfunctioning of the hydraulic steering conv the various new passagewaysfor hydraulic follow --against the pressure in the working chambers andwould be immediately dampened and stopped. Thus the hydraulic devicebesides functioning as a hydraulic steering motor, will function at alltimes to dampen out shimmy.

Severe obstruction in the path of the steering wheel when landing mightoffer undue stress in the working parts oi the hydrauliedevice, and

part 46' ofthe valve body connect the valve ports 68 and 84 with thelower annular channel in the valve body which communicates throughpassa'geway 12 with the space 1|, the spaces 68 and 1| outside of theupperand lower cylinder end walls 28 and 86 being thus always connectedwith the pressure fluid supply from the pipe 68, as with I the structureof Figures 3, 4 and 5. The slabbed upper part of the valve body has thediametrite'rsects the valve chamber 81 for communication cally extendingpassageway or port 65' which inoi the valve chamber with theworkingchambers relief or blow-off valves may therefore be pro- Y .vided. Theseblow-oil valves may lie-located in the hydraulic device abutments or inthe piston vanes. Figures 6 and 7 show a form ofblow-ofl valve providedin the vanes. In each vane a valve chamber 80 is provided having aconical seat 8| for a valve 82 in the form of a. conical plug which isnormally held against the seat by a spring 83 abutting the valve and adisc 84 secured in the end of the'valve chamber. Into opposite sides ofeach vane extend passages 85 and 85 which terminate in the valve chamber80 at the seat 8| to be normally shut oil by the .valve plug 42. If now,while the plane is landing or taxilng, the steering wheel is suddenlysubjected to a severe deflecting force, and the corresponding movementof the piston structure subjects the hydraulic fluid in' the workingchambers to ab-- normal sudden compression, the fluid forced through thepassages 85 and 85' will exert suflicent pressure against the conicalside of the blowhydraulicdevice may operate under normal conditions.

Instead oi having blow-oil valves in the vanes or abutments, a singleblow-oft valve may be embodied in the main valve structure V, as shownon Figures-8, 9 and 10. In this modified arrangement. the upper portionof the valve body 46 is slabbed oil on opposite sides to provide theports and 6-4 as'in Figures 3, 4 and s, but the lower portion 46- iscylindrical. The end of the. valve bore v48 in the valv stem iswidenedin the valve b dy to provide a valve chamber 81, and to provide aconical valve seat 81' in the cylindrical part 46. A conicalvalve plug88 normally en- 88 which abuts the valve and a tubular plug 86 extendinginto and seated in the upper end of the -'valve chamber 81, theplug-extending into the recess 68 of the plug 61 secured in the end wall28, the plug 86 thus-forming a bearing support for the valve structure.As was described in connection with the structure on Figure 3, in thestruc ture of Figures 8, 9, and 10 the plug-61 has the passageways 10connecting the space 68 with the in the cylinder structure when thevalve V is open, the valve plug 88 having the passageway 88'therethrough forfiow of fluid from the working chambers into the bore 48of the valve stem and through pipe 48 back to the reservoir R. Extendingthrough the cylindrical part 46- of the valve body, from the valve seat81', are the radial passageways or ports 9| and 9| and 92 and 92, and inthe zone of these passageways or ports, passageways 83 and 93 and 84 and94' are provided in the piston hub for registration with the portsthrough the valve body part 46' for connection of the respective workingchambers with the valve chamber 81, as clearly shown on Figure 9. Whenthe valve 88 is seated, the riorts in the valve body part 46 are closedto the valve chamber 81. When the valve 46 is in its fullyclosedposition, as shown on Figure 10, the ports. 8| 82 and 82' will be infull registration with the passageways 93, 83. 84 and 94, respectively,as shown on Figure 9, and as the r valve 46 is moved toward its fullyopen position, these ports will be moved out of communication with thepassageways.

If, while the valve 46 is in its'normal or fully closed position, thesteering wheel during landgages this seat and is held thereto by aspring annular channel 6| in the upper end of the valve obstructiontending to deflect the wheel. the cor-' responding movement of thepiston structure will subject the fluid in the working chambers to suchabnormal pressure ,that the fluid .through the ports in the valve bodypart 46" acting against the conical or inclined surface of the valveplug 88, will shift this valve-plug axially upwardly a ainst theresistance of the spring 89 so that the working chambers will beconnected with the fluid outflow bore 48 connected with the reservoirwhich is at atmospheric pressure and the piston structure will bemomentarily permitted free movement until the abnormal pressure shock isovercome-when the blow-ofl valve 48 will'again be closed' If the shockwas suflicient to turn the steering wheel and piston structure 'sufli-'ci'ently tomove the valve 46 for exposure of the passageways from theworking chamber to the valve ports 63 and 64, then the fluid flow underpressure .from the pump will enter the correpiston structure to followthe valve setting for reclosure of the valve 46 when setting movementstops.

I also provide simple but efllcient means for -preventing leakage pastthe piston of the piston body, and passageways 16' through thecylindrical 7 vanes. In the end of each vane are channels 86 whichextend radially, and longitudinally the full length of the vane, and inthese channels are sealing blades 91 for engaging the inner side of thecylinder wall I9. Ports 98 lead from the working chambers to thechannels and the inner ends of the blades are beveled so that thepressure of the hydraulic fluid will hold the blades outwardly inintimate sealing engagement with the cylinder wall.

I thus provide an efficient arrangement for power steering, by ahydraulic motor device, of the steering wheel of an airplane landinggear, with the hydraulic motor functioning also to dampen out shimmy. Ihave shown a practical and eflicient embodiment of the features of myinvention, but I do not desire to be limited to the exact construction,arrangement, and operation shown and described, as changes and modi-'fications may be made without departing from the scope of the invention.

I claim as follows: a

1. In a unitary rotary hydraulic shock ab-- sorber and steering motor inwhich a vaned Piston hub is oscillatable in hydraulic working chambersbetween the outer and inner end walls of a cylinder and hydraulic'abutments therein, a cylindrical valve chamber in the piston hub, acylindrical valve in said valve chamber, inner and outer abutments forthe ends of said valve, outer and inner circumferential channels in therespective ends of said valve, said valve being slabbed oif ondiametrically opposite sides to provide segmental inlet ports, portsextending through the piston hub between said valve cham ber and thehydraulic working chambers at opposite sides of the piston vanes, saidpiston hub having a shaft extending to the exterior of the cylinder andsaid valve having a hollow stem extending through said shaft to theexterior thereof, said valve having outlet ports therethroughcommunicating with theinterior of the hollow valve stem, a hydraulicfluid inlet space at the outer end of the cylinder structure havingcon-. nection with said outer circumferential channel and said segmentalinlet ports, said inlet and outlet ports being closed to the hydraulicwork'- ing chambers when said valve is in neutral position but beingopened to said chambers when said valve is rotated in either directionfrom itsneutral position for application of hydraulic pressure to thevanes for hydraulic rotation of the piston to follow the valve movementfor reclosure of. the inlet and outlet ports when rotation of the valveis stopped, said circumferential channels being connected by saidsegmental inlet ports whereby both ends of the valve head will besubjected to the fluid inflow pressure for axial balance of the valve.

2. In a unitary rotary hydraulic shock absorber and steering motor inwhich a vaned piston hub is oscillatable in hydraulic working chambersbetween the outer and inner end walls of a cylinder and hydraulicabutments therein, a cylindrical valve chamber in the piston hub, 'acylindrical valve in said valve chamber, inner and outer abutments forthe ends of said valve, outer and inner circumferential channels in there-- tending through said shaft to the exterior thereof, said valvehaving outlet ports therethrough communicating with the interior of thehollow valve stem, a hydraulic fluid inlet space at the outer end of thecylinder structure having connection with said outer circumferentialchannel and-said segmental inlet ports, said inlet and outlet portsbeing closed to the hydraulic working chambers when said valve is inneutral position but being opened to said chambers when said valve isrotated in either direction from its neutral position for application ofhydraulic pressure to the vanes for hydraulic rotation of the piston tofollow the valve movement for reclosure of the inlet andoutlet portswhen rotation of the valve is'stopped, said circumferential channelsbeing connected by said segmental inlet ports whereby both ends of thevalve head will be subjected to the fluid inflow pressure for axialbalance of the valve, the outer cylinder end wall being subjected to thepressure in said inlet space, a fluid space outside of the inner endwall of the cylinder and a connection from said space through the pistonhub to the inner circumferential channel in said valve, whereby thefluid Pressure against the outer sides of the cylinder end Wallswillbalance the pressure in the hydraulic chambers against the innersides of said end walIs.

3; In a rotary hydraulic steering motor in which a vaned piston isrotatable in hydraulic working chambers in a cylinder between abutmentson the cylinder, a cylindrical valve chamber in the piston hub, a mainvalve rotatable in said valve chamber, a first zone of flow passagewaysincluding ports in said valve and ports in, said piston, saidpassageways being closed to flow when said valve is in a neutralposition but being opened when said valve is rotated for flow of fluidfor causing rotation of said piston, a second zone of flow passagewaysincluding ports in said valve and ports in said piston, a relief valvewithin said main valve and a spring holding it in position for closureof said second zone passageways against normal fluid pressure when saidfirst zone passageways are closed by said main valve but said springyielding for movement of said valve to open saidsecond zone passagewaysduring abnormal fluid pressure when said first zone passageways areclosed by the main valve.

4. In a rotary hydraulic shock absorber and steering motor in which avaned piston is rotatable in hydraulic working chambers in a cylinderbetween abutments on the cylinder, a cylindrical valve chamber in thepiston hub, a main valve rotatable in said valvechamber, a first portingzoneincluding inlet and outlet ports in said main valve and inlet andoutlet ports through the piston hub for said working chambers, saidports, in said first porting zone being closed against flow when saidmain valve is in aneutral position but being opened for flowof fluidunder pressure into working chambers when said valve is rotated ineither direction from its neutral position for steering rotation of saidpiston, a second porting zone including inflow and outflow ports in saidmain valve and inflow and outflow ports in the piston hub for saidworking cham bers, an axially shiftable relief valve within said mainvalve, and spring means holding said valve closed to shut oflfflowthrough said second porting zone during normal fluid pressure in saidworking chambers when said first porting zone is closed against flow bysaid main valve, said spring steerin yielding to abnormal fluid pressurein said working chambers to permit unseating of said relief valve forr'elieiflow through said second porting,

z one. v A

5. In a rotary hydraulic shock absorber and motor in which a vanedpiston is rotatable in between abutments on the.cylinder, a cylindricalvalve chamber in the piston hub, a main valve rotatable in said valvechamber, a first porting zone including inlet and outlet ports in saidmain valve and inlet and outlet ports through the piston'hub for saidworking chambers, said ports' in said first porting zone being closedagainst flow when said mainvalve is in a neutral position but beingopened for flow of fluid under pressure into working chambers-when saidvalve is rotated in either direction from its neutral position forsteering rotation of said piston, a second porting zone includingoutflow ports in said main valve ydraulic working chambers in a cylindertion for steering rotation of said piston, a second porting zoneincluding outflow ports in said main valve and ports in the piston hubfor said working chambers, a fluid outflow passageway-in said main.valve to the exterior of the cylinder, and a relief valve interposed in,said outflow passageway and spring means for holding said relief valveseated to shut oil flow through said second porting zone during normalfluid pressure conditions in said working chambers while said main valveis in neutral position to close the said first porting zone, said springmeans yielding to abnormal pressure conditions for unseating of saidrelief valve by the abnormal pressure for opening of said second portingzone for flow of fluidfrom said hydraulic working chambers into saidoutflow passageway until normal pressure is reestablished, said reliefvalve having a passageway and ports in the piston hub for said workingchambers, a fluid outflow passageway in saidmain valve to the exteriorof the cylinder, a relief valve withinv said outflow passageway, andspring means normally holding said relief valve seated to shut oil flowthroughsaid second porting zone under normal hydraulic pressure in saidworking chambers when said first porting zone is closed by,

therethrough for outflow of fluid through said first porting z'one intosaid outflow passageway during seating of said relief valve and movementof said main valve out of its normal position.

7. In a rotary hydraulic shock absorber and steering motor in which avaned piston is rotatable in lwdrau lic working chambers in a cylin-'der between abutments on the cylinder, a cylindrical valve chamber inthe piston hub, a main valve rotatable in said valve chamber, a firstporting zone includinginlet and outlet ports in said main valve andinlet and outlet rts through the piston hub for said working 0 ambers',said ports in said flrst porting zone being closed'against flowwhen saidmain valve is in a neutral position but being opened for flow of fluidunder pressure into-working chambers when said valve is rotated ineither direction from its neutral position for steering rotation of saidpiston, a second porting. zone including ports in said main able inhydraulic working chambers in a cylinder between abutments on thecylinder, a cylindrical valve chamber in the piston hub, a main valverotatable in said valve chamber, a first porting zone including inletand outlet ports in said main-valve and inlet and outlet ports throughthe piston hub for said working chambers, said ports in said flrstporting zone being closed against flow when said main valve is in aneutral posi-v tion but being opened for flow of fluid under pressureinto working chambers when said valve is rotated in either directionfrom its neutral posi-' valve and ports through the piston hubwhichports are in register'when said main valve is in neutral position, arelief valve within said main valve, and spring means seating saidrelief valve to shut oii flow through said second zone when the pressurein said working chambers is normal but responding to abnormal pressurefor unseating of the relief valve by the abnormal pressure for ilowbetween working chambers to relieve the abnormal pressure.

- HARRY L. CHISHOL1\L JR.

